"""
Copyright (C) 2017 Open Source Robotics Foundation

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""


class CityElement(object):
    """A city element is an object that belongs to a city and that may
    be visited by a generator to create the contents for a file.
    We are using a vistor pattern here to do the double-dispatching and
    the entry point is the `accept` message"""

    def accept(self, generator):
        raise NotImplementedError()
